well on a key board your common is one of the two
arrows to match the pad up for up, down for down ect... then
s=b
e=a
a=y
w=x
or use a,w,s,z for the arrows and use
l=b
p=a
k=y
o=x
but really its up to you, just match up the controller layout.
most people put start and select on 1/2 and l and r on the left/right shift.